Instead of saying character boundary, should we leave the word "character" for the concept that can be represent by a code point, i.e. a single TIS-620 character. And then use "cluster" or (in Unicode term) "grapheme cluster" for the combining character sequence like กี่, กู้ or กำ

One pattern that is always an issue is whether "กำ" or "น้ำ" one or two clusters. In OpenOffice.org and Microsoft Office, they treat the pattern as one unit.